1. Field of the Invention
This invention relates to color television recording and playback systems. In a primary applicationn the invention relates to the playing back of the information recorded on color film in a color television format. Another application of the invention relates to the photographic recording of live scenes using a conventional motion picture camera with the resultant images scanned and converted into color television images.
2. Description of Prior Art
A variety of approaches have been used for the recording and playback of color television information. Film systems represent an attractive approach to the recording and playback of color television information. They have high information density, relatively low cost, and can be used in relatively simple home movie cameras and played back on home color television receivers.
Existing color television playback systems from film have various practical and economic problems. The commercial studio systems use expensive color television camera systems requiring three carefully registered television camera tubes. Other approaches use encoded systems where the color information is encoded onto black and white film. One such encoding format is described in U.S. Pat. No. 3,378,633 issued to A. Macovski. In this patent the red and blue information are encoded as amplitude modulation of high frequency gratings. This system requires a relatively high resolution television camera to resolve the high frequency color carriers. Also, the luminance resolution must be degraded somewhat to prevent high-frequency luminance detail from appearing in the high-frequency color signals.
One solution to this problem is the use of separate recorded frames for the luminance and chrominance information as in a system called EVR. The EVR system is described in a publication by Peter C. Goldmark entitled, "Color Electronics Video Recording" which appeared in the Journal of the Society of Motion Picture and Television Engineers, Vol. 79, August, 1970, pp. 677-686. In this system an electron beam recorder is used to record separate luminance and encoded chrominance frames at 60 fields/sec. A cathode ray tube flying spot scanner is used to read out the luminance and chrominance signals. This system as described is limited to the use of pre-recorded material since the consumer cannot conveniently make his own encoded film with an electron beam recorder. U.S. Pat. No. 3,535,992 issued to P.C. Goldmark, et. al. represents a relatively complex approach to providing the desired format with optical recording.
A preferred system for encoding color information on a black and white format is given in pending application, "Color Television Encoding and Decoding System," Ser. No. 820,602, filed Aug. 1, 1977, assigned to the same assignee as the present invention and having the present four inventors as four of the co-inventors. In this application the readout is accomplished using uniform film motion with two relatively inexpensive line scanner arrays rather than using relatively expensive frame scanners or cathode ray tube line scanners. The line arrays are used with simplified synchronization systems since they do not have the non-uniform scan velocities of cathode ray tubes.
These black and white encoded systems, however, all require relatively extensive modifications to the movie camera and are thus incompatible with existing movie cameras. Only the first system, using the three registered color cameras, uses conventional color film and thus an unmodified movie camera. These cameras are, however, very expensive.
Some systems in the prior art have used a cathode ray tube flying spot scanner, for example U.S. Pat. No. 2,776,335 issued to A. E. Mann and U.S. Pat. No. 3,378,635 issued to P.C. Goldmark, et. al. These CRT's were used in color film scanners in U.S. Pat. Nos. 3,619,485 and 3,569,612 issued to D. J. Cross, et. al. and U.S. Pat. No. 3,619,483 issued to W. K. Boots, et. al. These systems often use modified raster scans so as to simplify the film motion. Here a cathode ray tube is imaged onto the film with the transmitted light applied to three photomultiplier tubes through appropriate color filters. These systems have a variety of problems including the lag in the CRT phosphor, the poor color response of the phosphor and the inadequate brightness of the CRT. In addition the components involved are bulky and expensive. If a CRT is used with any type of striped encoded format, the non-uniform scan velocity necessitates synchronization information throughout the image region. Synchronization information of this type results in various chroma errors due to luminance information interfering with the synchronization signal. For example a black region in the scene results in a loss of synchronization information.
The new CCD photosensitive arrays are excellent candidates for film scanning because of their small size and low potential cost. In addition, they have extremely accurate scanning speeds determined solely by the clock frequency. These devices are described in a paper entitled "Imaging Devices Using the Charge-Coupled Concept," in Proc. IEEE, Vol. 63, pp. 38-67, January 1975. They have been described as two-dimensional color TV cameras in U.S. Pat. No. 3,971,065 issued to B. E. Bayer and in U.S. Pat. No. 4,007,488 issued to M. Moishita. These two-dimensional camera devices, however, are extremely expensive and difficult to fabricate free of defects. Their use in consumer products appears to be a number of years away.
The single line CCD devices, however, are presently available at relatively low costs. A color film scanner using solid state line scan devices is described in U.S. Pat. No. 3,952,328 issued to C. H. Biber. In this patent, color film using the conventional frame rates of 18-24 frames per second is used. Since these rates are incompatible with the television scan rates, the scanning system of the color TV receiver is modified in accordance with the film rate. This results in a very complex television receiver for use with different scan rates. In addition, the resultant image will have significant flicker. The color decomposition is accomplished using dichroic mirrors and three line scan arrays, one for each color. These must be positioned very accurately to avoid misregistration and its associated color errors. They would probably require periodic readjustment.
A system using a single line scan array is described in U.S. Pat. No. 3,953,885 also issued to C. H. Biber. As in the previous patent this system requires a specially modified color television receiver. It is used to scan color film of the type employing longitudinal film stripe triplets. The color triplets on the film are imaged onto a single line array with the individual elements of the array carefully registered with the individual colors on the film. This use of a single array for all of the information requires a large number of elements in the array. Since the resultant scanned signal is used for luminance and chrominance, the color triads must occur at a frequency beyond the luminance bandwidth. Thus the number of elements in the line array is approximately three times the number of luminance picture elements.
In addition to the high resolution requirements of the line array, it must be exactly registered to the color stripes on the film. This may be disturbed by factors such as film shrinkage and various mechanical variations. Again, these problems are aggravated by the use of a color triad repetition frequency which is above the luminance bandwidth.